xx

MECHANICAL BEHAVIOUR OF ALUMINIUM

BASED METAL MATRIX COMPOSITES

REINFORCED WITH SiC AND ALUMINA

A

Thesis

Submitted in fulfilment of the requirement for the award of

degree of

MASTER OF ENGINEERING

IN

PRODUCTION & INDUSTRIAL ENGINEERING

Submitted By:

Pulkit Bajaj

Roll No. 800982019

Under the Guidance of

Mr. Yogesh Kumar Singla Mr. Anil Kalra

Lecturer Lecturer

M.E.D M.E.D

Thapar University Thapar University

Patiala-147004 Patiala-147004

DEPARTMENT OF MECHANICAL ENGINEERING

THAPAR UNIVERSITY

PATIALA-147004, INDIA

ACKNOWLEDGEMENT

I am highly grateful to the authorities of Thapar University, Patiala for providing this

opportunity to carry out the thesis work.

I would like to express a deep sense of gratitude and thank profusely to my thesis guide

Mr. Anil Kalra (Lecturer) & Mr. Yogesh Singla (Lecturer) for his sincere & invaluable

guidance and suggestions which inspired me to submit thesis report in the present form.

I am highly thankful to Dr. Rahul Chhibber for their invaluable guidance & morale

boosting support from time to time. I am also thankful to Dr. Ajay Batish, Head of

Department, Department of Mechanical Engineering, Dr. S.K Mohapatra, Dean of

Academic Affairs and other faculty members and workshop staff of Mechanical

Engineering Department, Thapar University, Patiala for their intellectual support.

My special thanks to my family members and friends who constantly encouraged me to

complete this work.

Pulkit Bajaj

(800982019)

ii

ABSTRACT

Aluminium alloys are widely used in aerospace and automobile industries due to their low

density and good mechanical properties, better corrosion resistance and wear, low thermal

coefficient of expansion as compared to conventional metals and alloys. The excellent

mechanical properties of these materials and relatively low production cost make them a

very attractive candidate for a variety of applications both from scientific and

technological viewpoints. The aim involved in designing metal matrix composite

materials is to combine the desirable attributes of metals and Ceramics.

Present work is focused on the study of behaviour of Aluminium Cast Alloy (LM6) with

SiC and Al O composite produced by the stir casting technique. Diff erent % age of 2 3

reinforcement is used. Tensile test, Hardness Test, Impact test performed on the samples

obtained by the stir casting process. X-ray Diffraction was performed to know the

presence of the phases of reinforced material.

Hardness tester is employed to evaluate the interfacial bonding between the particles and

the matrix by indenting the hardness with the constant load and constant time. X-ray

Diffraction was performed to know the presence of the phases of reinforced material.

Scanning electron microscopy was done to know the distribution of SiC/Alumina

particles in Aluminium alloy.

iii

CONTENTS

DESCRIPTIONS PAGE NO.

CERTIFICATE i ACKNOLEGEMENT ii ABSTRACT iii CONTENTS iv LIST OF FIGURES vii

xi LIST OF TABLES

CHAPTER 1 INTRODUCTION 1

1.1 INTRODUCTION 1 1.1.1 Advantages of Aluminium 1

1.2 ALUMINIUM ALLOYS 4

1.2.1 Cast Aluminium Alloys 4

1.2.2 Wrought Aluminium Alloys 5 1.3 DESIGNATION OF ALUMI NIUM ALLOYS 5

1.4 APPLICATION OF ALUMINUM ALLOYS 6

1.5 INTRODUCTION TO COMPOSITE MATERIALS 6

1.6 CLASSIFICATION OF COMPOSI TES 7

1.6.1 Natural Composites 7

1.6.2 Man-Made Composites 8

MATRIX (PRIMARY PHASE) 1.7 8

REINFORCEMENT (SECONDARY PHASE) 1.8 8

1.9 PROCESSING OF MMCS 9

1.9.1 Liquid Metal Techniques 10

1.9.1.1 Stir Casting Pr ocess 10

1.9.1.2 Infiltration 11

1.9.1.3 Gas Pressure Infiltration 11

1.9.1.4 Squeeze Casting Infiltration 12

1.9.1.5 Pressure Die Infiltration 13

1.10 SILICON CARBIDE AS REINFORCEMENT 13

1.10.1 Properties of Silicon Carbide 14

1.11 ALUMINA AS REINFORCEMENT 14

1.11.1 15 Properties of Alumina

iv

1.12 TENSILE STRENGTH 15

1.12.1 Yield Point 16

1.12.2 Ultimate Tensile Strength 18

1.12.3 Measures of Ductility (Elongation and Reduction of Area) 18

1.13 HARDNESS 20

1.14 TOUGHNESS 20

1.14.1 Impact Toughness 21

1.15 X- RAY POWDER DIFFRACTION 22

1.16 SCANNING ELECTRON MICROSCOPE (SEM) 23

CHAPTER 2 LITERATURE REVIEW 25

2.2 GAPS FOUND FROM LITERATURE 29

CHAPTER 3 PROBLEM 30

FORMULATION

3.1 OBJECTIVES OF PRESENT WORK 30

CHAPTER 4 EXPERIMENTAL WORK 31

4.1 EXPERIMENTAL SET UP USED IN STI R CASTING OPERATION 35

4.2 EXPERIMENTAL PROCEDURE 36

4.2.1 Preparation of Samples 36

4.2.2 Following procedure was followed after the casting 37

preparation

CHAPTER 5 RESULTS AND 39

DISCUSSION

5.1 IMPACT TEST RESULTS 39

5.2 HARDNESS TEST 41

5.3 TENSILE STRENGTH TEST 42

5.3.1 Stress vs. Strain Curves 43

5.3.2 Yield Strength Comparison 49

5.3.3 Ultimate Tensile Strength Result 51

5.3.4 Length Elongation Compar ison 52

5.4 RESULTS OF SEM 54

5.6 XRD ANALYSIS RESULT 55

v

CHAPTER 6 CONCLUSIONS 67

6.1 CONCLUSIONS 67

6.2 SCOPE OF FUTURE WORK 67

REFERENCES 68

vi

LIST OF FIGURES

FIGURE NO. PAGE

NO.

1.1 Aluminium Used In Ship 1

1.2 Aluminium Used In Aeroplane 1

1.3 Aluminium Used in Mar ine 2

1.4 Aluminium Used in Industries 2

1.5 Aluminium Used in Wires 2

1.6 Aluminium Used in Rescue Blanket 2

1.7 Aluminium Used as Bar 3

1.8 Aluminium Used in Packaging 3

1.9 Classification of Aluminium Alloy 4

1.10 Abalone shell 7

1.11 Scallop shell 7

1.12 Man made composites used in Airplane and Plywood 8

1.13 Laboratory stir casting set up 11

1.14 Gas Pressure Infiltration 12

1.15 Squeeze Casting Infiltration 12

1.16 Silicon Carbides as reinforcement 13

1.17 Alumina as reinforcement 15

1.18 Stress Strain Curve of Ductile Material 16

1.19 Fracture Point of Ductile and Brittle mater ial 19

1.20 Temperature Vs Toughness Graph 21

1.21 Izod Charpy Test Machine 21

1.22 SEM working 24

1.23 SEM beam 24

4.1 Muffle Fur nace 31

4.2 Graphite Stirrer 32

4.3 Full View of Gr aphite Stirrer with Steel Rod 32

4.4 Sieve Analysis Tester 33

4.5 Belt Grinder 33

4.6 Power Hack Saw 34

4.7 Drilling Machine used for Stirring Purpose 34

vii

4.8 Graphite Crucible used to keep molten metal in muffle 35

furnace

4.9 Flow Chart Exper imental Techniques followed 35

4.10 Schematic view of setup of Stir Casting 36

4.11 Mould and cast product after casting 37

5.1 Comparison of Impact Strength with %age variation of SiC 40

5.2 Comparison of Impact Strength with %age variation of Al O 40 2 3

5.3 Comparison of Impact Strength with %age variation of 40

mixture Al O & SiC 2 3

5.4 Comparison the Hardness with wt. % variation of SiC 41

5.5 Comparison the Hardness with wt. % variation of Al O 42 2 3

5.6 Comparison the Hardness with wt. % variation of combined 42

Al O & SiC 2 3

5.7 Tensile Strength Specimens of dif ferent composition 43

5.8 Stress vs. Strain Curves for LM 6 Alloys 44

5.9 Stress vs. Strain Curves for LM 6 Alloys with 2.5 % SiC 44

5.10 Stress vs. Strain Curves for LM 6 Alloys with 5 % SiC 44

5.11 Stress vs. Strain Curves for LM 6 Alloys with 7.5 % SiC 45

5.12 Stress vs. Strain Curves for LM 6 Alloys with 10% SiC 45

5.13 Stress vs. Strain Curves for LM 6 Alloy with 2.5% Al O 45 2 3

5.14 Stress vs. Strain Curves for LM 6 Alloy with 5% Al O 46 2 3

5.15 Stress vs. Strain Curves for LM 6 Alloy with 7.5% Al O 46 2 3

5.16 Stress vs. Strain Curves for LM 6 Alloy with 10 % Al O 46 2 3

5.17 Stress vs. Strain Curves for LM 6 Alloy with 5% T (Sic & 47

Al O ) 2 3

5.18 Stress vs. Strain Curves for LM 6 Alloy with 10% T (SiC & 47

Al O ) 2 3


Al O ) 2 3


Al O ) 2 3

5.21 Comparison the Yield Str ength with wt. % var iation of SiC 49

5.22 Comparison the Yield Str ength with wt. % var iation of Al O 49 2 3

viii

5.23 Comparison the Yield Strength with wt. % variation of Al O 50 2 3

& SiC

5.24 Comparison the Ultimate Tensile Strength with wt. % 51

variation of SiC


variation of Al O 2 3


variation of SiC & Al O mixture 2 3

5.27 Comparison the Elongation with wt. % variation of SiC 52

5.28 Comparison the Elongation with wt. % variation of Al O 53 2 3

5.29 Comparison the Elongation with wt. % variation of Mixture 53

of SiC & Al O 2 3

5.30 Microscopic View of 2.5 % SiC Reinforced in LM6 100 X, 54

500 X, 1000 X

5.31 Microscopic View of 7.5 % SiC Reinforced in LM6 100 X, 54

500 X, 1000X

5.32 Microscopic View of 10 % Alumina Reinforced 100 X, 500 54

X, 1000 X

5.33 Microscopic View of 15 % SiC & Al O Reinforced in 54 2 3

100X, 500 X, 1000 X

5.34 X-ray diffraction pattern of the alloy with 2.5% wt. SiC 55

5.35 X-ray diffraction pattern of the alloy with 5% wt. SiC 56

5.36 X-ray diffraction pattern of the alloy with 7.5% wt. SiC 57

5.37 X-ray diffraction pattern of the alloy with 10% wt. SiC 58

5.38 X-ray diffraction pattern of the alloy with 2.5% wt. Al O 59 2 3

5.39 X-ray diffraction pattern of the alloy with 5% wt. Al O 60 2 3


5.41 X-ray diffraction pattern of the alloy with 10% wt. Al O 62 2 3

5.42 X-ray diffraction pattern of the alloy with 5% wt. SiC & 63

Al O 2 3


Al O 2 3


ix

Al O 2 3


Al O 2 3

x

LIST OF TABLES

Table No. Title Page

No.

1.1 Designation of Cast Aluminium alloys 5

1.2 Designation of Wrought Aluminium alloys 5

1.3 Temper Designation System 6

1.4 Alloys confor ms to British Standards 1490 LM6 Cast Aluminium 6

1.5 Application of Aluminium alloys 6

1.6 Reinforcement of Aluminium Alloy 9

1.7 Comparison between Reinforced & Un- Reinforced Aluminium 9

Alloy

1.8 Properties of Silicon Carbide 14

1.9 Properties of Alumina 15

4.1 List of Equipment used for Stir Casting Operation 31

4.2 Composition of Samples 37

5.1 Results of I mpact Test 39

5.2 Results of Micro hardness Test 41

5.3 Tensile Strength Results 43

5.4 X-ray diffraction of the alloy with 2.5 % wt. SiC 56

5.5 X-ray diffraction of the alloy with 5 % wt SiC 56

5.6 X-ray diffraction of the alloy with 7.5 % wt. SiC 57

5.7 X-ray diffraction of the alloy with 10 % wt. SiC 58


5.9 X-ray diffraction pattern of the alloy with 5 % wt. Al O 60 2 3

5.10 X-ray diffraction pattern of the alloy with 7.5 % wt. Al O 61 2 3

5.11 X-ray diffraction pattern of the alloy with 10 % wt Al O 62 2 3

5.12 X-ray diffraction of the alloy with 5% wt. SiC & Al O 63 2 3




xi

CHAPTER 1 INTRODUCTION

1.1 INTRODUCTION

The aim involved in designing metal matrix composite materials is to combine the

desirable attributes of metals and ceramics. The addition of high strength, high modulus

refractory particles to a ductile metal matrix produce a material whose mechanical

properties are inter mediate between the matrix alloy and the ceramic reinforcement. [1]

Aluminium is the most abundant metal in the Earth's crust, and the third most abundant

element, after oxygen and silicon. It makes up about 8% by weight of the Earth's solid

surface. Due to easy availability, High strength to weight r atio, easy machinability,

durable, ductile and malleability Aluminium is the most widely used non-ferrous metal in

2005 was 31.9 million tonnes. [2]

1.1.1 Advantages of Aluminium

I. Light Weight, Strong and Long-lasting

Aluminium is a very light metal with a specific weight of 2.7 gm/cm , about a third that of 3

steel. For example the use of aluminium in vehicles reduces dead-weight and energy

consumption while increasing load capacity. Its strength can be adapted to the application

required by modifying the composition of its alloys. The application of light weight,

strong and long lasting aluminium alloy is shown in Figure 1.1 & 1.2. [3]

Figure 1.1: Aluminium Used In Ship Figure 1.2: Aluminium Used In Aeroplane [3 ] [3 ]

II. Highly Corrosion Resistant

Aluminium naturally generates a protective oxide coating and is highly corrosion resistant.

It is particularly useful for applications where pr otection and conservation are required.

The application of highly corrosion resistance aluminium alloy is shown in Figure 1.3 & 1.4 . [3]

1

Figure 1.3: Aluminium Used in Marine Figure 1.4: Aluminium Used in Industries [ 3 ] [3]

III. Excellent Heat and Electricity Conductor

Aluminum is an excellent heat and electricity conductor and in relation to its weight is

almost twice as good a conductor as copper. This has made aluminium the most

commonly used material in major power transmission lines. The application of excellent

heat and electricity conductor is shown in Figur e 1.5. [3]

Figure 1.5: Aluminium Used in Wires [3 ]

IV. Good Reflective Properties

Aluminium is a good reflector of visible light as well as heat, and that together with its

low weight makes it an ideal mater ial for reflectors, for example, light fittings or rescue

blankets. The application of good r eflective pr operties is shown in Figure 1.6. [3].

Figure 1.6: Aluminium Used in Rescue Blanket [3 ]

2

V. Very Ductile

Aluminium is ductile and has a low melting point and density. In a molten condition it can

be pr ocessed in a number of ways. Its ductility allows products of aluminium to be

basically formed close to the end of the product. The application of ductility is shown in

Figure 1.7. [3]

Figure 1.7: Aluminium Used as Bar [3]

VI. Completely Impermeable and Odourless

Aluminium foil, even when it is rolled to only 0.007 mm thickness, is still completely

impermeable and let’s neither light aroma nor taste substances out. Moreover, the metal

itself is non- toxic and releases no aroma or taste substance which makes it ideal for

packaging sensitive products such as food or phar maceuticals. The application of [3]

completely impermeable and odourless aluminium alloy is shown in Figure 1.8. [3]

Figure 1.8: Aluminium Used in Packaging [3]

VII. Totally Recyclable

Aluminium is 100 percent recyclable with no downgrading of its qualities. The re-melting

of aluminium requires little energy: only about 5 percent of the energy required to produce

the primar y metal initially is needed in the recycling process. Pure Aluminium has also [3]

some limits according to properties so to enhance Aluminium properties aluminium alloys

are used.

3

1.2 ALUMINIUM ALLOYS

Selecting the right alloy for a given application entails considerations of its tensile

strength, density, ductility, formability, workability, weld ability, and corrosion resistance.

Aluminium alloys are alloys in which aluminium (Al) is the predominant metal.

The typical alloying elements ar e copper, magnesium, manganese, silicon, and zinc. There

are two pr incipal classifications, namely casting alloys and wrought alloys, both of which

are further subdivided into the categories heat-treatable and non-heat-treatable. About 85%

of aluminium is used for wrought products, for example rolled plate, foils and extrusions.

Cast aluminium alloys yield cost effective products due to its low melting point, although

they generally have lower tensile strengths than wrought alloys. The most important cast

aluminium alloy system is Al-Si, where the high levels of silicon (4.0% to 13%) contribute

to give good casting character istics. Aluminium alloys are widely used in engineer ing

structures and components where light weight or corrosion resistance is requir ed. Wrought

aluminium alloy s are used in the shaping processes: rolling, forging, extrusion, pressing,

stamping. Cast Aluminium alloys are comes after sand casting, permanent mould casting,

die casting, investment casting, centrifugal casting, squeeze casting and continuous

casting Aluminium alloys are classified as shown in Figure 1.9. . [4]

Aluminium Alloys

Wrought Alloys Cast Alloys

Figure 1.9: Classification of Aluminium Alloy

1.2.1 Cast Aluminium Alloys

Aluminium and its alloys are used in a var iety of cast and wrought for m and conditions of

heat treatment. Forgings, sections, extrusions, sheets, plate, strip, foils and wire are some

of the examples of wrought form while castings are available as sand, pressure and gravity

die-castings e.g. Al-Si and Al- Mg alloys. The designation of Cast Aluminium alloy is [4]

shown in Table 1.1.

4

Table 1.1: Designation of Cast Aluminium alloys [4 ]

Alloy Designation Details 1XX.X 99% pure Aluminium

2XX.X Cu containing alloy

3XX.X Si, Cu/Mg containing alloy 4XX.X Si containing alloy 5XX.X Mg containing alloy 6XX.X Zn containing alloy

1.2.2 Wrought Aluminium Alloys

To meet various requirements, aluminium is alloyed with copper, manganese, magnesium,

zinc and silicon as major alloying elements. The designation of wrought aluminium alloy

is shown in Table 1.2. [4]

Table 1.2: Designation of Wrought Aluminium alloys [4]

Alloy designation Details

1XXX 99% pure Aluminium

2XXX Cu containing alloy

3XXX Mn containing alloy

4XXX Si containing alloy

5XXX Mg containing alloy

6XXX Mg and Si containing alloy

7XXX Zn containing alloy

8XXX Other alloys

1.3 DESIGNATION OF ALUMINIUM ALLOYS

The Aluminium Association of Amer ica has classified the wrought aluminium alloys

accor ding to a four-digit system. The classification is adopted by the I nternational Alloy

Development System (I ADS) . Table 1.3 gives the basis of designation of wrought and cast

aluminium alloys in the four-digit system. The f ir st digit identifies the alloy type the

second digit shows the specific alloy modification. The last two digits indicate the specif ic

aluminium. Aluminium Alloy in present Thesis work is shown in Table 1.4.

5

Table 1.3: Temper Designation System [5 ]

Letter Condition of alloy F As-fabricated O Annealed T4 Solution treated T6 Solution treated and aged

Table 1.4: Alloys conforms to British Standards 1490 LM6 Cast Aluminium [5]

Chemical Composition Weight Percentage 0.1 Copper

Magnesium 0.10 max. Silicon 11

Iron 0.6 Manganese 0.5 max

Nickel 0.1 max Zinc 0.1 max Tin 0.05 max

Titanium 0.2 max Aluminium Remainder

1.4 APPLICATION OF ALUMINUM ALLOY

The application of aluminium alloy is shown in Table 1.5

Table 1.5: Application of Aluminium alloys [6]

Aluminium Alloy Alloy Charact eristics Common Use

1050/1200 Non heat-treatable. Good formability, weld ability and corrosion resistance Food and Chemical Industry

2014 Heat-treatable. High strength. Non wieldable. Poor corrosion resistance Airframes

Non-heat-treatable. Medium strength work hardening alloy. Good Vehicle paneling, structures exposed

5251/5052 weld ability, formability and corrosion to marine atmospheres, mine cages.

resistance. Heat-treatable. Medium strength alloy. Good Architectural extrusions (internal and

6063 weld ability and corrosion resistance. Used for external) window frames, irrigation intricate profiles. pipes.

Heat-treatable. Properties very similar to 6082. Stressed structural members, bridges,

6061/6082 Preferable as air quenchable, therefore has less cranes, roof trusses, beer barrels

distortion problems. Not notch sensitive. Heat-treatable. Age hardens naturally, therefore

Armored vehicles, military bridges, 7075 will recover properties in heat-affected zone

motor cycle and bicycle frames after welding. Susceptible to stress corrosion..

1.5 INTRODUCTION TO COMPOSITE MATERIALS

Composites ar e materials in which two phases are combined, usually with strong

interfaces between them. They usually consist of a continuous phase called the matrix and

discontinuous phase in the for m of fibers, whiskers or particles called the r einforcement.

6

Considerable interest in composites has been generated in the past because many of their

properties can be descr ibed by a combination of the individual properties of the constituent

phases and the volume fraction in the mixture.

Composite materials ar e gaining wide spread acceptance due to their character istics of

behaviour with their high strength to weight ratio. The interest in metal matr ix composites

(MMCs) is due to the relation of str ucture to properties such as specific stiffness or

specific strength. Like all composites, aluminium matrix composites are not a single

material but a family of materials whose stiffness, density and thermal and electrical

properties can be tailored . composites materials are high stiffness and high strength, low

density, high temperature stability, high electrical and ther mal conductivity, adjustable

coefficient of thermal expansion, corrosion r esistance, improved wear resistance etc. The

matr ix holds the reinfor cement to form the desir ed shape while the reinforcement

improves the overall mechanical properties of the matrix. When designed properly, the

new combined material exhibits better strength than would each individual mater ial. [7]

1.6 CLASSIFICATION OF COMPOSITES

Particulate composites consist of particles immer sed in matrices such as alloys and

ceramics. They are usually isotropic since the particles are added randomly. Particulate

composites have advantages such as improved strength, increased operating temperature

and oxidation resistance etc. Typical examples include use of aluminium particles in

rubber, silicon carbide particles in aluminium. Flake composites provide advantages such

as high out-of plane flexur al modulus, higher str ength, and low cost. [7]

1.6.1 Natural Composites

under natural composites. E.g. bones, wood, shells, Several natural materials can be grouped

pearlite (steel which is mixture of a phase FeC). The example of Natural composites are

shown in Figure 1.10 & 1.11.

Figure 1.10: Abalone shell (CaCO ) Figure 1.11: Scallop shell [7] [7] 3

7

1.6.2 Man-Made Composites

Man-made composites are produced by combining two or more materials in definite

proportions under controlled conditions. e.g. Mud mixed straw to produce stronger mud

mortar and bricks, Plywood, Chipboards, Decorative lam inates etc. The example of Man [7]

made composites are shown in Figure 1.12.

Figure 1.12: Man made composites used in Airplane and Plywood [7 ]

1.7 MATRIX (PRIMARY PHASE)

The selection of suitable matrix alloys is mainly determined by the intended application of

the composite material.

I. For the development of light metal composite materials that are mostly easy to process,

conventional light metal alloys are applied as matrix materia ls. Mainly Aluminium Alloy is used

for Light weight Composites.

II. The matrix is the monolithic material into which the reinforcement is embedded, and is

completely continuous. This means that there is a path through the matrix to any point in the

material, unlike two materials sandwiched together.

III. In structural applications, the matrix is usually a lighter metal such as Aluminium, magnesium,

or titanium, and provides a compliant support for the reinforcement. In high temperature

applications, cobalt and cobalt-nickel alloy matric es are common. [ 8]

1.8 REINFORCEMENT (SECONDARY PHASE)

The reinforcement material is embedded into the matr ix. The r einforcement does not

always serve a purely structural task (reinforcing the compound) , but is also used to

change physical properties such as wear resistance, friction coefficient, or thermal

conductivity. The reinforcement can be either continuous, or discontinuous. Discontinuous

MMCs can be isotropic, and can be worked with standard metalworking techniques, such

as extrusion, forging or rolling. In addition, they may be machined using conventional

techniques, but commonly would need the use of poly crystaline diamond tooling (PCD).

Continuous reinforcement uses monofilament wir es or fibers such as carbon fiber or

silicon car bide. Because the fibers are embedded into the matrix in a certain direction, the

8

result is an anisotropic structure in which the alignment of the mater ial affects its strength.

One of the first MMCs used boron filament as reinforcement. Discontinuous

reinforcement uses "whiskers", short fibers, or particles. The most common r einforcing

materials in this categor y are alumina and silicon carbide . [8]

Examples of some current application of composites include the tires, diesel piston, brake-

shoes and pads. Examples of different reinforcement of aluminium alloy are shown in

Table 1.6. The Al O and SiC are used as reinforcement in present experimental work. 2 3

Comparison between reinforced & unreinforced aluminium alloy is done in Table 1.7.

Table 1.6: Reinforcement of Aluminium Alloy [8 ]

Non Metallic Metallic

Alumina Beryllium

Boron Niobium

Silicon Carbide Stainless Steel

Table 1.7 : Comparison between Reinforced & Un - Reinforced Aluminium Alloy [8 ]

Advantages Disadvantages

Compared to Un- Reinforced Aluminium Alloys

Higher Specific Strength Lower toughness and ductility

Higher Specific Stiffness More Expensive and complicated Production Method

Improved High Temperature Creep Resistance

Improved Wear Resistance

Compared To Polymer Matrix Composites

Higher Transverse Strength Less developed Technology Higher Toughness Smaller Database Technology

Higher Damage Tolerance Higher Cost Improved Environmental Resistance

Higher Electrical and Thermal Conductivity Higher Temperature Capability

Compared Ceramic Matrix Composites

Higher Toughness and Ductility Infer ior High Temperature Capability Ease of Fabrication

Lower Cost

1.9 PROCESSING OF MMCS

Accordingly to the temperature of the metallic matrix during processing the fabr ication of

MMCs can be classified into three categories:

9

(a) Liquid phase processes,

(b) Solid state processes, and

(c) Two phase (solid-liquid) processes

1.9.1 Liquid Metal Techniques

Liquid state fabrication of Metal Matrix Composites involves incorporation of dispersed

phase into a molten matr ix metal, followed by its Solidification. In order to provide high

level of mechanical pr operties of the composite, good inter facial bonding (wetting)

between the dispersed phase and the liquid matrix should be obtained. Wetting

improvement may be achieved by coating the dispersed phase p articles ( fibers). Proper

coating not only r educes inter facial energy, but also prevents chemical interaction between

the dispersed phase and the matrix. The simplest and the most cost effective method of

liquid state fabr ication is Stir Casting . [9]

The methods of liquid state fabrication of Metal Matrix Composites are:

Stir casting

I nfiltration

Gas Pressure Infiltration

Squeeze Casting Infiltration

Pressure Die Infiltration

Deposition Processes

1.9.1.1 Stir Casting Process

Stir Casting is a liquid state method of composite mater ials fabr ication, in which a

dispersed phase (ceramic particles, short fibers) is mixed with a molten matr ix metal by

means of mechanical stirring. The liquid composite material is then cast by conventional

casting methods and may also be processed by conventional Metal forming technologies

. The Stir Casting set up is shown in Figure 1.13. [9]

Figure 1.13: Stir casting set up

10

1.9.1.2 Infiltration

Infiltration is a liquid state method of composite materials fabr ication, in which a

preformed dispersed phase e.g. ceramic particles, fibers, are soaked in a molten matrix

metal, which fills the space between the dispersed phase inclusions. The motive force of

an infiltration process may be either capillar y for ce of the dispersed phase or an external

pressure applied to the liquid matr ix phase. Infiltr ation is one of the methods of

preparation of tungsten-copper composites. [9]

The principal steps of the technology are as follows:

Tungsten powder preparation with average particle size of about 1-5 micron.

Optional step: Coating the powder with nickel. Total nickel content is about

0.04%.

Mixing the tungsten powder with a polymer binder.

Compacting the powder by a molding method. Compaction should provide the

pr edetermined porosity level of the tungsten structure.

Solvent rebinding and sinter ing the green compact at 1204- 1315°C in hydrogen

atmosphere for 2 hrs. Placing the sintered part on a copper plate or powder in the

infiltr ation/sinter ing furnace.

I nfiltration of the sintered tungsten skeleton porous structure with copper at 110-

1260 °C in either hydrogen atmosphere or vacuum for 1 hour.

1.9.1.3 Gas Pressure Infiltration

Gas pressure infiltration is a forced infiltr ation method of liquid phase fabrication of metal

matr ix composites, using a pressurized gas for applying pressure on the molten metal and

forcing it to penetrate into a preformed dispersed phase . [9]

Figure 1.14: Gas Pressure Infiltration [9]

11

Gas Pressure I nfiltr ation method is used for manufacturing lar ge composite parts. This

method allows using non-coated fibers due to short contact time of the fibers with the hot

metal. I n contrast to the methods using mechanical force, Gas Pressure Infiltration results

in low damage of the fibers. The Figure 1.14 shows the Schematic view of Gas pressure

infiltr ation.

1.9.1.4 Squeeze Casting Infiltration Squeeze casting infiltration is a forced infiltration method of liquid phase fabrication of

metal matrix composites, using a ram for applying pressure on the molten metal and

forcing it to penetrate into a dispersed phase, placed into the lower fixed mold part.

Squeeze casting . Infiltration method is similar to the squeeze casting technique used for [9]

metal alloys casting. Figure 1.15 shows the Schematic view of squeeze casting Infiltr ation.

Figure 1.15: Squeeze Casting Infiltration [9]

Squeeze casting infiltration process has the following steps:

A per for m of dispersed phase is placed into the lower fixed mold half.

A molten metal in a predetermined amount is poured into the lower mold half.

The upper movable mold half (ram) moves downwards and forces the liquid metal

to infiltrate the perform.

The infiltrated material solidifies under the pr essure.

The part is removed from the mold by means of the ejector pin.

12

1.9.1.5 Pressure Die Infiltrat ion

Pressure Die I nfiltration is a forced infiltration method of liquid phase fabr ication of Metal

Matrix Composites, using a Die casting technology, when a prefor med dispersed phase is

placed into a die which is then filled with a molten metal entering the die through a sprue

and penetrating into the per for m under the pressure of a movable piston. [9 ]

1.10 SILICON CARBIDE AS REINFORCEMENT

Silicon Carbide is the only chemical compound of carbon and silicon. It was or iginally

produced by a high temperature electro-chemical reaction of sand and carbon. Silicon

carbide is an excellent abrasive and has been produced and made into gr inding

wheels and other abrasive pr oducts for over one hundred years. Today the mater ial has

been developed into a high technical grade ceramic with very good mechanical quality

properties . [10]

It is used in abrasives, refractoriness, ceramics, and numerous high-performance

applications. The material can also be made an electrical conductor and has applications in

resistance heating, flame igniters and electronic components. Silicon carbide is composed

of tetrahedral of carbon and silicon atoms with strong bonds in the crystal lattice. This

produces a very hard and strong material. Silicon particles are shown in Figure 1.16. [1 0]

Figure 1.16: Silicon Carbides as reinforcement [10 ]

1.10.1 Properties of Silicon Carbide

• Low density

• High strength

• Low thermal expansion

• High thermal conductivity

• High hardness

• High elastic modulus

13

• Excellent thermal shock resistance

• Superior chemical inertness

Detailed properties of SiC are shown in Table 1.8.

Table 1.8: Properties of Silicon Carbide

Properties Value Properties

Melting Point (°C) 2200-2700 Linear coefficient of expansion (10 K) -6

Limit of application (°C) 1400-1700 Fracture toughness (MPa-m ) 1/ 2 Moh’s Hardness 9 Crystal structure

Density (g/cm ) 3.2 Linear coefficient of expansion 3 (10 K) -6

1.11 ALUMINA AS REINFORCEMENT

Aluminium oxide, commonly referred to as alumina, possesses str ong ionic inter atomic

bonding giving rise to its desirable mater ial characteristics. It can exist in several

crystalline phases which all revert to the most stable hexagonal alpha phase at elevated

temper atures. This is the phase of particular inter est for structural applications and the

material available from Accuratus. Alpha phase alumina is the strongest and stiffest of the

oxide cer amics. Its high hardness, excellent dielectric properties, refractor iness and good

thermal properties make it the material of choice for a wide range of applications. High

pur ity alumina is usable in both oxidizing and r educing atmospheres to 1925°C. Weight

loss in vacuum ranges fr om 10 to 10 g/cm sec over a temperature range of 1700° to –7 –6 2

2000°C.

It resists attack by all gases except wet fluorine and is resistant to all common r eagents

except hydr ofluoric acid and phosphoric acid. The composition of the ceramic body can be

changed to enhance par ticular desirable material characteristics . An example would be [11]

additions of chr ome oxide or manganese oxide to improve hardness and change color.

Other additions can be made to improve the ease and consistency of metal films fired to

the ceramic for subsequent brazed and soldered assembly. Alumina particles ar e shown in

Figure 1.17.

Figure 1.17: Alumina as reinforcement [1 1]

14

1.11.1 Properties of Alumina

Detailed properties of Alumina are shown in Table 1.9 are shown on next page. [11]

Table 1.9 : Properties of Alumina

99.5% Aluminium Oxide

Mechanical Unit of SI

measure Unit

Density gm/cc (lb/ft ) 3.89 3

Porosity % 0

Elastic GPa 375

Modulus (lb/in x10 ) 2 6 Shear GPa 152

Modulus (lb/in x10 ) 2 6 Bulk GPa 228

Modulus (lb/in x10 ) 2 6 Poisson’s - 0.22

Ratio MPa•m Fracture 4 1 /2

Toughness Hardness Kg/mm 1440 2

Compressive MPa 2600

Strength (lb/in x10 ) 2 3 1.12 TENSILE STRENGTH

Tensile properties dictate how the material will react to forces being applied in tension. A

tensile test is a fundamental mechanical test where a carefully prepared specimen is loaded

in a very controlled manner while measur ing the applied load and the elongation of the

specimen over some distance. Tensile tests are used to determine the modulus of elasticity,

elastic limit, elongation, proportional limit, and reduction in area, tensile strength, yield

point, yield strength and other tensile properties. The main product of a tensile test is a

load versus elongation cur ve which is then converted into a stress versus strain curve.

Since both the engineering stress and the engineering strain are obtained by dividing the

load and elongation by constant values (specimen geometry infor mation), the load-

elongation curve will have the same shape as the engineering stress-strain curve. The

stress-strain curve relates the applied stress to the resulting strain and each material has its

own unique stress-strain curve. [12]

15

A typical engineering stress-strain cur ve is shown below Figure 1.18. I f the true stress,

based on the actual cross- sectional area of the specimen, is used, it is found that the stress-

strain curve increases continuously up to fractur e. They are tabulated for common

materials such as alloys, composite materials, ceramics, plastics, and wood. Tensile

strength is defined as a stress, which is measured as force per unit area. [12]

Figure 1.18: Stress Strain Curve of Ductile Material [1 2]

1.12.1 Yield Point

In ductile materials, at some point, the stress-str ain cur ve deviates from the str aight-line

relationship and Law no longer applies as the strain increases faster than the stress. From

this point on in the tensile test, some per manent deformation occurs in the specimen and

the material is said to react plastically to any further increase in load or stress. The

material will not return to its original, unstressed condition when the load is removed. In

brittle materials, little or no plastic deformation occurs and the material fractures near the

end of the linear-elastic portion of the curve . [12]

With most materials there is a gradual transition from elastic to plastic behavior, and the

exact point at which plastic deformation begins to occur is hard to determine. Therefore,

var ious criteria for the initiation of yielding are used depending on the sensitivity of the

strain measurements and the intended use of the data. For most engineering design and

specification applications, the yield strength is used. The yield strength is defined as the

stress required producing a small, amount of plastic deformation. The offset yield strength

is the stress corresponding to the intersection of the stress-str ain curve and a line parallel

16

to the elastic part of the curve offset by a specified strain (in the US the offset is typically

0.2% for metals and 2% for plastics).

To determine the yield strength using this offset, the point is found on the strain axis

(x-axis) of 0.002, and then a line parallel to the stress-strain line is drawn. This line will

intersect the stress-strain line slightly after it begins to cur ve, and that inter section is

defined as the yield strength with a 0.2% offset. A good way of looking at offset yield

strength is that after a specimen has been loaded to its 0.2 percent offset yield strength and

then unloaded it will be 0.2 percent longer than before the test. Even though the yield

strength is meant to represent the exact point at which the material becomes permanently

deformed, 0.2% elongation is considered to be a tolerable amount of sacrifice for the ease

it creates in defining the yield strength . [12]

Some materials such as gray cast iron or soft copper exhibit essentially no linear -elastic

behavior. For these materials the usual practice is to define the yield str ength as the stress

required to produce some total amount of strain.

True elastic limit is a very low value and is related to the motion of a few hundred

dislocations. Micro strain measurements are required to detect strain on order of 2

x 10 - 6 in/in.

Proportional limit is the highest stress at which stress is directly proportional to

strain. It is obtained by observing the deviation from the straight-line portion of the

stress-strain curve.

Elastic limit is the greatest str ess the mater ial can withstand without any

measurable per manent strain remaining on the complete release of load. It is

determined using a tedious incremental loading-unloading test procedure. With the

sensitivity of strain measurements usually employed in engineering studies (10 -

4in/in), the elastic limit is greater than the proportional limit. With increasing

sensitivity of strain measur ement, the value of the elastic limit decreases until it

eventually equals the true elastic limit deter mined from micro strain measurements.

Yield st rength is the stress required to produce a small-specified amount of plastic

deformation. The yield strength obtained by an offset method is commonly used

for engineering purposes because it avoids the pr actical difficulties of measur ing

the elastic limit or proportional limit. [12]

17

1.12.2 Ultimate Tensile Strength

The ultimate tensile str ength (UTS) or, more simply, the tensile strength, is the maximum

engineer ing stress level r eached in a tension test. The strength of a material is its ability to

withstand external forces without breaking. In brittle mater ials, the UTS will at the end of

the linear -elastic portion of the stress-strain curve or close to the elastic limit. In ductile

materials, the UTS will be well outside of the elastic portion into the plastic portion of the

stress-strain curve. [12]

On the str ess-strain curve above, the UTS is the highest point where the line is

momentarily flat. Since the UTS is based on the engineering str ess, it is often not the same

as the breaking strength. In ductile materials strain hardening occurs and the stress will

continue to increase until fracture occurs, but the engineer ing stress-strain curve may show

a decline in the str ess level before fracture occurs. This is the result of engineering stress

being based on the or iginal cross-section area and not accounting for the necking that

commonly occurs in the test specimen. The UTS may not be completely representative of

the highest level of stress that a mater ial can support, but the value is not typically used in

the design of components anyway . [12]

For ductile metals the current design practice is to use the yield strength for sizing static

components. However, since the UTS is easy to determine and quite reproducible, it is

useful for the purposes of specifying a mater ial and for quality control purposes. On the

other hand, for brittle mater ials the design of a component may be based on the tensile

strength of the material. [12]

1.12.2 Measures of Ductility (Elongation and Reduction of Area)

The ductility of a mater ial is a measure of the extent to which a material will defor m

before fracture. The amount of ductility is an important factor when considering for ming

operations such as rolling and extrusion. It also provides an indication of how visible

overload damage to a component might become before the component fractures. Ductility

is also used a quality control measure to assess the level of impur ities and proper

processing of a mater ial. [12]

18

The conventional measures of ductility are the engineer ing strain at fr acture (usually

called the elongation) and the reduction of area at fracture. Both of these properties are

obtained by fitting the specimen back together after fracture and measur ing the change in

length and cross-sectional area. Fracture or breaking Point of ductile or brittle material is

shown in Figure 1.19. [12]

Figure 1.19: Fracture Point of Ductile and Brittle material [12]

Elongation is the change in axial length divided by the original length of the specimen or

portion of the specimen. It is expressed as a percentage. Because an appr eciable fraction of

the plastic deformation will be concentrated in the necked region of the tensile specimen,

the value of elongation will depend on the gage length over which the measurement is

taken. The smaller the gage length the greater the large localized strain in the necked

region will factor into the calculation. Therefore, when reporting values of elongation, the

gage length should be given. One way to avoid the complication from necking is to base

the elongation measurement on the unifor m strain out to the point at which necking

begins. This works well at times but some engineer ing stress-strain curve are often quite

flat in the vicinity of maximum loading and it is difficult to precisely establish the strain

when necking starts to occur. Reduction of area is the change in cross-sectional ar ea

divided by the original cross-sectional area. This change is measured in the necked down

region of the specimen. Like elongation, it is usually expressed as a percentage. [12 ]

19

1.13 HARDNESS

Hardness is the resistance of a material to localized deformation. The term can apply to

deformation from indentation, scratching, cutting or bending. I n metals, ceramics and most

polymers, the deformation considered is plastic deformation of the sur face. For elastomers

and some polymers, hardness is defined at the resistance to elastic defor mation of the

surface. The lack of a fundamental definition indicates that hardness is not be a basic

property of a mater ial, but rather a composite one with contributions from the yield

strength, work hardening, true tensile strength, modulus, and others factors. Hardness

measurements are widely used for the quality control of materials because they are quick

and consider ed to be nondestructive tests when the marks or indentations produced by the

test are in low stress areas. There are a large variety of methods used for determining the

har dness of a substance. A few of the more common methods are introduced below. [13]

1.14 TOUGHNESS

The ability of a metal to defor m plastically and to absorb energy in the process before

fractur e is termed toughness. The emphasis of this definition should be placed on the

ability to absorb energy before fracture. Recall that ductility is a measure of how much

something deforms plastically before fracture, but just because a material is ductile does

not make it tough. The key to toughness is a good combination of strength and ductility. A

material with high strength and high ductility will have more toughness than a material

with low strength and high ductility. Therefore, one way to measure toughness is by

calculating the area under the stress strain curve from a tensile test. This value is simply

called “mater ial toughness” and it has units of energy per volume. Mater ial toughness

equates to a slow absorption of energy by the material. There are several variables that

have a profound influence on the toughness of a mater ial. These variables are:

Str ain rate (rate of loading)

Temperatur e

Notch effect

A metal may possess satisfactory toughness under static loads but may fail under dynamic

loads or impact. As a rule ductility and, therefore, toughness decrease as the rate of

loading increases. Temperature is the second var iable to have a major influence on its

toughness. As temperature is lowered, the ductility and toughness also decrease. The thir d

var iable is termed notch effect, has to due with the distribution of stress. [14]

20

1.14.1 Impact Toughness

The impact toughness of a material can be determined with a Charpy or Izod test. Impact

properties are not directly used in fracture mechanics calculations, but the economical

impact tests continue to be used as a quality control method to notch sensitivity and for

comparing the relative toughness of engineering materials. For both tests, the specimen is

broken by a single overload event due to the impact of the pendulum. A stop pointer is

used to r ecord how far the pendulum swings back up after fractur ing the specimen. The

impact toughness of a metal is determined by measuring the energy absorbed in the

fractur e of the specimen.

This is simply obtained by noting the height at which the pendulum is released and the

height to which the pendulum swings after it has struck the specimen. The height of the

pendulum times the weight of the pendulum produces the potential energy and the

difference in potential energy of the pendulum at the start and the end of the test is equal

to the absorbed energy. Since toughness is greatly affected by temperature, a Charpy or

Izod test is often repeated numerous times with each specimen tested at a different

temper ature. This produces a graph of impact toughness for the material as a function of

temper ature.

I mpact toughness versus temperatur e graph for steel is shown in the Figure 1.20. It can be

seen that at low temperatures the material is more br ittle and impact toughness is low. At

high temperatures the material is more ductile and impact toughness is higher. Izod

Charpy test machine is used in Figure 1.21. [14]

Figure 1.20: Temperature Vs Toughness Graph Figure 1.21: Izod Charpy Test Machine [ 14] [14 ]

21

1.15 X-RAY POWDER DIFFRACTION

X-ray diffraction r elies on the dual wave/particle natur e of X-r ays to obtain information

about the structure of crystalline mater ials. A primary use of the technique is the

identification and characterization of compounds based on their diffraction patter n.The

dominant effect that occur s when an incident beam of monochromatic X-rays interacts

with a target material is scattering of those X-rays from atoms within the target material.

In materials with regular structure (i.e. crystalline), the scattered X-rays undergo

constructive and destructive inter fer ence. This is the process of diffr action. The dif fraction

of X-rays by crystals is described by Bragg’s Law, n =2d sinT. The directions of possible

diffr actions depend on the size and shape of the unit cell of the mater ial. The intensities of

the diffracted waves depend on the kind and arrangement of atoms in the crystal structure.

However, most materials are not single cr ystals, but are composed of many tiny

crystallites in all possible orientations called a polycr ystalline aggregate or powder. When

a powder with randomly oriented crystallites is placed in an X-r ay beam, the beam will see

all possible inter atomic planes. If the experimental angle is systematically changed, all

possible diffraction peaks from the powder will be detected. The focusing (or Bragg-

Brentano) diffractometer is the most common geometry for diffraction instruments.

This geometry offers the advantages of high resolution and high beam intensity analysis at

the cost of very precise alignment requirements and carefully prepared samples.

Additionally, this geometr y requires that the source-to-sample distance be constant and

equal to the sample-to-detector distance. Alignment errors often lead to difficulties in

phase identification and improper quantification. A mis-positioned sample can lead to

unacceptable specimen displacement error s. Sample flatness, roughness, and positioning

constraints preclude in-line sample measurement. Additionally, traditional XRD systems

are often based on bulky equipment with high power requirements as well as employing

high powered X- ray sources to increase X-ray flux on the sample, therefore increasing the

detected diffraction signals from the sample. These sources also have large excitation

areas, which are often disadvantageous for the diffraction analysis of small samples or

small sample features.

Polycapillary X- ray optics can be used to overcome many of these drawbacks and

constraints to enhance XRD applications. Polycapillar y collimating optics convert a highly

divergent beam into a quasi- parallel beam with low divergence. They can be used to form

a Parallel Beam XRD instrument geometry which greatly reduces and removes many

22

sources of errors in peak position and intensity inherent to the parafocusing geometry,

such as sample position, shape, roughness, flatness, and transparency. Polycapillar y

focusing optics collect X-rays from a divergent X-ray source and direct them to a small

focused beam at the sample sur face with diameters as small as tens of micr ometers for

micro X-ray diffraction applications of small samples or small specimen features. Both

types of polycapillary optics dir ect ver y high X-ray intensities to the sample sur face, such

that XRD systems employing optics can use low power X-ray sources, reducing

instrument size, cost, and power requirements. [15]

X-ray diffraction using X-ray optics has been applied to many different types of

applications including thin film analysis, sample texture evaluation, monitoring of

crystalline phase and structure, and investigation of sample stress and strain.

When a focused X-ray beam interacts with these planes of atoms, part of the beam is

transmitted, part is absorbed by the sample, part is refracted and scattered, and part is

diffr acted. This high voltage accelerates the electrons, which then hit a target, commonly

made of copper. When these electrons hit the target, X -rays are produced. The wavelength

of these X rays is character istic of that target. These X-rays are collimated and directed

onto the sample, which has been ground to a fine powder (typically to produce particle

sizes of less than 10 microns). A detector detects the X-ray signal; the signal is then

processed either by a microprocessor or electronically, converting the signal to a count

rate. Changing the angle between the X-ray source, the sample, and the detector at a

controlled rate between preset limits is an X-ray scan. When an X- ray beam hits a sample

and is diffracted, we can measure the distances between the planes of the atoms. [15]

1.16 SCANNING ELECTRON MICROSCOPE (SEM)

SEM stands for scanning electron microscope. The SEM is a microscope that uses

electrons instead of light to form an image. Since their development in the early 1950's,

scanning electron microscopes have developed new areas of study in the medical and

physical science communities. The SEM has allowed researchers to examine a much

bigger variety of specimens.SEM working i.s shown in Figure 1.22 & 1.23

The scanning electron microscope has many advantages over traditional microscopes. The

SEM has a large depth of field, which allows more of a specimen to be in focus at one

time. The SEM also has much higher resolution, so closely spaced specimens can be

magnified at much higher levels. Because the SEM uses electromagnets rather than lenses,

the researcher has much more control in the degree of magnif ication. All of these

23

advantages, as well as the actual strikingly clear images, make the scanning electron

microscope one of the most useful instruments in r esearch today.

Figure 1.22: SEM working [16 ]

Figure 1.23: SEM beam [16 ]

Detectors collect these X-rays, backscattered electrons, and secondary electrons and

convert them into a signal that is sent to a screen similar to a television screen. This

produces the final image. [1 6]

24

LITERATURE REVIEW CHAPTER 2

This chapter presents a r eview of the literature data available on the effect of var ious

reinforcement types, their size and volume fraction, ageing behavior with Al based MMC’s.

Metal matrix composites are a combination of two phases, matrix and the reinforcement.

Matr ices can be selected from a number of Aluminium alloys e.g. AA 2000, 6000, 7000,

A356 and many reinforcement types SiC, B C, Al O , AlN, and C etc. are available in 4 2 3

different sizes, mor phologies (particulates, short fibers, long fibers and platelets) and volume

fractions. These reinforcements can be combined with the dif ferent matrices, resulting in

lar ge composite systems. Furthermore, several different pr ocessing routes, such as powder

metallurgy, stir casting, squeeze casting, hot extrusion etc.

N. Chawla, J.J. Williams, G. Piotrowski, and R. Saha [2003] [12]

Authors investigated the tensile str ength processes in discontinuously reinforced aluminium

(DRA).In this exper iment author varies the average particle size (6-23 micro meter), Heat

treatment is also given. Conclusion of this paper is that as particle size increases Tensile

strength decreases. Heat treatment increases the tensile strength.

Manoj Singla, D. Deepak Dwivedi, Lakhvir Singh, Vikas Chawla[2009] [17]

In this author studied to develop aluminium based silicon car bide particulate MMCs with an

objective to develop a conventional low cost method of producing MMCs and to obtain

homogenous dispersion of ceramic material. To achieve these objectives two method of stir

casting technique has been adopted and subsequent property analysis has been made.

Aluminium (98.41% C.P) and SiC (320-grit) has been chosen as matrix and reinforcement

mater ial r espectively. Exper iments have been conducted by varying weight fraction of SiC

(5%, 10%, 15%, 20%, 25%, and 30%), while keeping all other parameters constant. An

incr easing trend of hardness and impact strength with increase in weight percentage of SiC

has been observed. The best results (maximum hardness 45.5 BHN & maximum impact

strength of 36 N-m.) have been obtained at 25% weight fraction of SiCp.

I. A. Ibrahim, F. A. Mohamed, E. J. Lavernia [ 2001] [1 8]

In this review author studied the mechanical properties that can be obtained with metal

matrix composites by var ying reinforcement percentage by 0, 10, 15, 20% and taking

different alloy AA 6061, AA 2014, AA 356. Conclusion of this paper is by increasing

reinforcement % age yield strength, ultimate strength is increasing but elongation of a Alloy

decreases.

25

D. J. Lloyd [1994] [19]

This r eview has primarily been concerned with the factors influencing the micro structural,

mechanical properties relationship of composites shows the effect of differ ent reinforcement.

In this author study differ ent reinforcement effect on different alloy are considered.

Conclusions of this paper are elongation of composites decreases as increases percentage of

reinforcement and tensile strength are increases.

L. Ceschini , G. Minak , A. Morri [2005] [20]

In this paper, the tensile pr operties and the low-cycle fatigue behavior of the 7005 aluminium

alloy reinforced with 10 volume % of Al O particles and 6061 aluminium alloy reinforced 2 3

with 20 volume % of Al O particles wer e studied. The tensile ductility was strongly affected 2 3

by the material in homogeneity, mainly related to the particles size and distribution. No

significant variation of the tensile strength and ductility with temperature was observed up to

150 C, while at 250 C strength significantly decreased, and ductility increased. o o

S.V. Prasad and R. Asthana[2004] [21]

This paper gives an overview of the tribological behavior of Al MMCs reinforced with hard

particles, short fiber s, and solid lubricants, and the technologies for producing automotive

parts from these novel materials. The emphasis has been on developing affordable Al MMCs,

reinforced with SiC and Al2O3, that will reduce the weight and increase the engine

efficiency, and thereby reduce fuel consumption and vehicle emissions.. Considerable

reduction in wear and friction is achieved by use of these particulates. Further more, increased

cylinder pressures (and therefore, higher engine perfor mance) are possible because Al MMCs

can withstand high mechanical and thermal loads, and reduce heat losses by permitting closer

fit that can be achieved because of lower thermal expansion coefficient of Aluminum MMCs.

P.K Rohatgi, J.K Kim, R.Q.Guo, D.P.Robertson, and M.Gajdardziska[2002] [22]

Investigated the effect of aging characteristics of aluminium alloy A356 and an aluminium

alloy A356 containing hollow spher ical fly ash par ticles were studied using optical

microscopy, transmission electron micr oscopy (TEM), energy dispersive X-ray (EDX)

spectroscopy, hardness tests, and compressive tests.. As the density of the composite is lower

than that of the base alloy due to the presence of hollow particles, the composites have a

higher specific strength and specific hardness compared to the matrix. Even though the

hardness of the as- cast composite was higher than that of the base alloy, no significant

change in the aging kinetics was observed, due to the presence of spherical fly ash particles

in the matr ix. Aging times of the order of 104 to 105 seconds were required to reach the peak

hardness (92 HRF) and compressive strength (376 MPa) in both the A356–5 wt. % fly ash

26

composite and the matrix alloy.

The possible effects of shape and hollowness of particles, the interface between the matrix

and the particles, the low modulus of the particles, and the micro cracks formed on the

surface o f hollow fly ash particles on the kinetics of the age hardening of aluminium alloy

A356.

S. Balasivanandha Prabu , L. Karunamoorthy, S. Kathiresan, B. Mohan[ 2006] [23]

In the pr esent study, high silicon content aluminium alloy–silicon car bide metal matrix

composite material, with 10% SiC were successfully synthesized, using different stirring

speeds and stirr ing times. The microstructure of the produced composites was examined by

optical microscope and scanning electron microscope. The Br inell hardness test was

perfor med. Increase in stir ring speed and stirring time resulted in better distribution of

particles.

The hardness test r esults also revealed that stirring speed and stirr ing time have their effect

on the hardness of the composite. The unifor m hardness values were achieved at 600 rpm

with 10 min stirring. But beyond certain stir speed the properties degraded again.

M. Kok[2004] [24]

In this author examined AA 2024 aluminium alloy metal matrix composites (MMCs)

reinforced with three different sizes and weight fr actions of Al O particles up to 30 wt. % 2 3

were fabricated by a vortex method and subsequent applied pressure. The effects of Al O 2 3

particle content and size of particle on the mechanical properties of the composites such as

hardness and tensile strength were investigated. Scanning electron micr oscopic observations

of the microstructures revealed that the disper sion of the coarser sizes of par ticles was more

unifor m while finer particles led to agglomeration of the particles and porosity. The r esults

show that the hardness and the tensile strength of the composites increased with decreasing

size and increasing weight fraction of particles.

G. B. Veeresh Kumar1, C. S. P. Rao, N. Selvaraj, M. S. Bhagyashekar[2010] [25]

Author examine the base matrix and the reinforcing phase for the present studies selected

were AA 6061, AA 7075 and particles of Al O and SiC of size 20 µm. It can be obser ved 2 3

that the densities of composites are higher than that of their base matrix, further the density

incr eases with increased percentage of filler content in the composites. it can be observed

that the tensile strength of the composites are higher than that of their base matrix also it can

be obser ved that the increase in the filler content contributes in increasing the tensile strength

of the composite. In microstructure studies it can be observed that, the distributions of

reinforcements in the respective matr ix are fairly uniform.

27

Daniel B. Miracle [2000] [26]

In Air Force Research Laboratory author studied 6092/SiC/17.5p & 2009/SiC/15p-T4 for

F16 aircraft Door and body purposes. It can be observed that the densities of composites are

higher than that of their base matrix, further the density increases with increased percentage

of filler content in the composites.

A. Daouda, W. Reif [2002] [27]

The author had studied the influence of Al2O3 particulates on the precipitation and

hardening behavior of the A356 Al O composites . It was found that the MgAl O spinel 2 3 2 3

formed at the interface led to Mg depletion in the matrix and subsequently to lesser age

hardening in the composites. Therefore, it was necessary for the composite matrix to have a

higher Mg concentration prior to casting to achieve the same level of hardening in the

composite as in the unreinforced. The hardening kinetics is enhanced by Al2O particulates

because the precipitation preferentially develops on the dislocation lines that increased due to

coefficient of thermal expansion mismatch between the matrix and reinforcement.

Hailong Wang [2008] [28]

The author was investigated; SiC particulate-reinforced Al composites were prepared by

powder metallurgy (PM) method and conventional atmospheric sinter ing. Scanning electron

microscope (SEM), X-r ay diffraction (XRD) techniques were used to character ize the

sintered composites. The effect of temperature on the density, hardness, str ength, and

microstructure of composites. Detailed failure behavior was analyzed. They had found that

the segregation of SiC appeared at higher temperature. The highest micro hardness of 80MPa

occurred at 700 C. The strength tended to increase with the increasing temperature due to

the formation of Al Cu. Both ductile and brittle fracture features were observed. 2

Z. M. El-Baradie [2007] [29]

Investigated 7020 aluminium alloy unreinforced and reinforced with 5 and 10% volume

fraction SiC particulates. The aging behaviour of the unreinfor ced and reinforced materials

was studied for both natural and artificial aging at 170°C. The results show that the

incorporation of 5 and 10 vol. % of SiCp can be improved considerably by natural or

artificial aging. Also, the effect of deformation for both unreinforced and composite alloys

was studied. The results show that the deformation altered the aging precipitation sequence

significantly the greater the deformation, the higher the dislocation densities and hence, the

faster the precipitation. Generally, defor mation accelerated aging and hence, peak hardness

occurred earlier. Also, appreciable increase in hardness and faster kinetics were obtained by

the introduction of thermomechanical pr ocessing to these alloys.

28

2.2 GAPS FOUND FROM LITERATURE

The extensive review of literature carr ied out for the present study reveals that a lot of work

has been reported to enhance the properties of Aluminium metal matrix composites through

stir casting or by any other process. The wor k car ried out by different researchers can be

categor ized in to the following broad classes:

I. Very limited amount of work has been repor ted which explains the factors affecting

mechanical properties like Tensile strength and Impact strength of Aluminium matrix

composites.

II. Very limited work on combined effect of Alumina and Silicon Carbides on aluminium

metal matrix composites properties have done.

29

CHAPTER 3 PROBLEM FORMULATION

3.1 OBJECTIVES OF PRESENT WORK

The problem is to study the tensile strength behaviour of Al-SiC/Alumina metal matrix

composite (MMC) of aluminium alloy of gr ade LM6 with addition of varying percentage

composition of SiC particles and Alumina made by stir casting technique. The tensile

strength and Toughness, Hardness like mechanical properties will also be taken into

consider ation. For the achievement of the above, an experimental set up is prepared where all

the necessar y inputs were made. The aim of the exper iment is to study the effect of variation

of the percentage composition to predict the mechanical properties of the metal matrix

composites (MMC). The experiment was carried out by prepar ing the sample of differ ent

percentage composition by stir casting technique. The present work emphasizes the literature

review of Al-Si alloys and its composites. There are many manufactur ing processes to form

composites commercially. But the technique adopted here is rapid solidification process. The

stir forming is newly developed technique and still under progress for its commercialization

in developing countr ies like I ndia. The objectives of pr esent proposal ar e as follows:

To prepare the cost-effective MMC material by taking Al-Si alloy with matrix ceramic

par ticulate like silicon carbide as reinforced phase using stir casting technique.

To analyze the micro structural characteristics of the as cast material.

Tensile str ength, Impact strength & Hardness measurements of the as prepared MMCs.

CHAPTER 4 EXPERIMENTAL WORK

4.1 EXPERIMENTAL SET UP USED IN STIR CASTING OPERATION Equipments used to perform the Stir Casting operation and testing of composites is shown

in Table 4.1.

Table 4.1 : List of Equipment used for Stir Casting Operation

S. No. Equipments Used S. No. Equipments Used

1 Radial drilling machine 6 Universal Testing Machine

2 Graphite Crucible/ mould 7 Hardness testing machine

3 Graphite Stirrer 8 Scanning electron microscope

4 Muffle Furnace 9 Power Hacksaw

5 Stainless steel rod (SS3l6) of diameter 12mm, Length 600mm 10 Impact Toughness Machine

The equipments used dur ing exper imental work are shown in Figure 4.1 to Fig. 4.9.

I. Muffle Furnace

Muffle Fur nace was used to heat the mater ial to desired temperatures by conduction,

convection, or blackbody radiation from electrical resistance heating elements. A muffle

furnace (sometimes, retort furnace) in historical usage is a furnace in which the subject

material is isolated from the fuel and all of the products of combustion including gases

and flying ash. In our muffle furnace which is shown in Figure 4.1 maximum temperature

of 1100°C. was achieved.

Temperature Indicator

Controller

Figure 4.1 : Muffle Furnace

31

II. Stirrer

The function of a stirrer was to agitate liquids for speeding up reactions. Stirrer was

designed to homogenous mixing of liquid, oilment, solution, viscous material and solid-

liquid.

Graphite Stirrer

Stainless Steel Bolt

Figure 4.2 : Graphite Stirrer

Stainless Steel Rod

Graphite Stirrer

: Figure 4.3 Full View of Graphite Stirrer with Steel Rod

III. Sieve Analysis Tester

A sieve analysis was used to assess the particle size distribution of a gr anular material.

The size distribution is often of critical importance to the way the mater ial performs in

use. A sieve analysis can be performed on any type of non-or ganic or organic granular

materials including sands, crushed rock, clays, granite, feldspars, coal, soil, a wide range

of manufactured powders, grain and seeds, down to a minimum size depending on the

exact method. In this experiment SiC and Alumina particles of 100 micron size were

used. Sieve analysis Tester was shown in Figure 4.4. was used to get desired granular

size.

32

Motor

Different Sieves used for gradation test

Figure 4.4 : Sieve Analysis Tester

IV. Belt Grinder

Belt Grinder was used for r esistant technology purposes to give a smooth, shiny finish to

manufactured products ( Aluminium Composites). Belt Gr inder is shown below in Figure

4.5.

Belt Drive

Belt

Figure 4.5: Belt Grinder :

V. Power Hack Saw

A power hacksaw (or electric hacksaw) was a type of hacksaw that was powered either by

its own electric motor. A hacksaw is a fine-tooth saw with a blade under tension in a

frame, used for cutting materials such as Aluminium alloy into small pieces so is to keep

the alloy into crucible. Power hacksaw is shown in Figure 4.6.

33

High Carbon Blade

Vice

Figure 4.6: Power Hack Saw

VI. Drilling Machine

This machine was used for rotating Stirrer at different speeds as shown in Figure 4.7.

Electr ic Motor

Speed Controller

Figure 4.7: Drilling Machine used for Stirring Purpose

VIII. Graphite Crucible

A crucible is a refractory container used for metal, glass, and pigment production as well

as a number of moder n laboratory processes, which can withstand temperatures high

enough to melt or otherwise alter its contents. Historically, they have usually been made

of clay, but they can be made of any mater ial with a higher temper ature resistance than

the substances they are designed to hold. Graphite crucible is shown in Figure 4.8.

34

Figure. 4.8: Graphite Crucible used to keep molten metal in muffle furnace

4.2 EXPERIMENTAL PROCEDURE

Starting Aluminium Alloy LM 6 with reinforcements SiC and Al O

2 3

Production of composite By Stir Casting

Tensile Strength Hardness Test Impact Test

XRD Micro Structure Study (SEM)

Result and Conclusion

Finish

Fi gu r e 4 . 9: F l o w C ha r t Ex pe r i m en t a l T e ch n i qu e s f ol l o we d

35

4.2.1 Preparation of Samples

Figure 4.10 : Schematic view of setup of Stir Casting [ 2 3 ]

1. Motor

2. Shaft

3. Molten Aluminium

4. Thermocouple

5. Particle Injection Chamber

6. Insulation Hard Chamber

7. Furnace

8. Graphite Crucible

Aluminium Alloy was melted in a crucible by heating it in a muffle furnace at 800°C for

three to four hours. The silicon carbide particles and Alumina particles were preheated at

1000 C and 900 C respectively for one to three hours to make their surfaces oxidised. The o o

furnace temperature was first raised above the liquidus temperature of Aluminium near

about 750 C to melt the Al alloy completely and was then cooled down just below the o

liquidus to keep the slurry in Semi solid state. Automatic stirr ing was carried out with the

help of radial drilling machine for about 10 minutes at stirring rate of 290 RPM. At this

stage, the preheated SiC particles and Alumina particles were added manually to the

vortex. In the final mixing pr ocesses the furnace temperature was controlled within 700 ±

10 C. After stirring process the mixture was pour in the other mould to get desired shape o

36

of specimen as shown in Figure 4.10. The presence of reinforcement throughout the

specimen was inspected by cutting the casting at different locations and under

microscopic examination. Same process was used for specimens with different

compositions of SiC and Alumina. Compositions of samples are shown in Table 4.2.

Figure 4.10: Mould and cast product after casting

4.2.2 Following procedure was followed after the casting preparation

1. Specimens, prismatic in shape with dimensions 10 mm × 10 mm × 10 mm for SEM,

XRD, Tensile strength specimen , Impact strength specimen 55×10×10, micro str ucture

and with dimensions 300 mm x 60mm x 30 mm (l x b x t) respectively were cut from the

cast composite.

2. Hardness of specimen was measured on hardness testing machine.

3. The SEM and XRD analysis was done for the samples.

4. Tensile Strength measure in Universal Testing Machine

6. Analyzing the micr ostructure of the specimens by SEM before the corrosion and after

the corrosion.

7. Impact strength measure by Izod & Charpy Machine

Table 4.2: Composition of Samples

Composition

Sample No. Aluminium(gm) SiC(gm) Zircon(gm) Remarks

1 1100 0 0 Weight of sample=1000 gm

2 990 26 0 SiC=2.5%

3 1050 55 0 SiC=5%

4 925 75 0 SiC=7.5%

5 1100 122 0 SiC=10%

6 975 0 25 Alumina=2.5%

7 990 0 52 Alumina =5%

37

8 1050 0 85 Alumina =7.5%

9 900 0 100 Alumina =10%

10 1020 27 27 SiC=2.5%+ Alumina =2.5%

11 1120 62 62 SiC=5%+ Alumina =5%

12 950 84 84 SiC=7.5%+ Alumina =7.5%

13 900 108 108 SiC=10%+ Alumina =10%

38

CHAPTER 5 RESULTS AND DISCUSSION

5.1 IMPACT TEST RESULTS

The Charpy impact test, also known as the Charpy v-notch test, is a standardized high strain-

rate test which deter mines the amount of energy absorbed by a material during fracture. This

absorbed energy is a measure of a given mater ial's toughness.

Table 5.1: Results of Impact Test

Trial Average

Serial Composites Force 1 2 3 4 5 Total Force No Nm Nm

1 Aluminum Alloy (LM6) 6.2 6.1 5.9 5.6 5.5 29.3 5.86

2 LM6 + 2.5 % SiC 7.3 7.2 7.3 6.8 6.7 35.3 7.06

3 LM6 + 5 % SiC 8.2 8 7.5 7.8 7.6 39.1 7.82

4 LM6 + 7.5 % SiC 8.8 7.9 7.5 8.6 7.6 40.4 8.08

5 LM6 + 10 % SiC 8.5 8.7 8.8 9.7 9.2 44.9 8.98

6 LM6 + 2.5 % Al O 6.5 6.5 6.7 6.8 6.6 33.1 6.62 2 3

7 LM6 + 5 % Al O 6.7 6.8 6.9 7.0 7.0 34.4 6.88 2 3

8 LM6 + 7.5 % Al O 7.1 7.0 7.0 6.9 7.2 35.2 7.04 2 3

9 LM6 + 10 % Al O 7.5 7.2 7.1 7.2 7.1 36.1 7.22 2 3

10 LM6 + (2.5+2.5) % 8.0 7.8 7.6 7.7 7.8 38.9 7.78

SiC+Al O 2 3

11 LM6 + (5+5) % SiC+Al O 8.2 8.5 8.9 9.2 9 43.8 8.76 2 3

12 LM6 + (7.5+7.5) % 8.8 9.1 9.3 9.1 9.5 45.8 9.16

SiC+Al O 2 3

13 LM6 + (10+10) % 9.2 9.3 9.4 9.0 9.9 46.8 9.36

SiC+Al O 2 3

39

10

8

6

4

2

0 Pure 2.5 % SiC 5 % SiC 7.5 % SiC 10 % SiC

Wt %age Reinforcement

Figure 5.1: Comparison of Impact Strength with %age variation of SiC

8 7 6 5 4 3 2 1 0

Pure 2.5 % Al2O3 5 % Al2O3 7.5 % Al2O3 10 % Al2O3

Wt %age reinforcement

Figure 5.2: Comparison of Impact Strength with %age variation of Al O 2 3

10

8

6

4

2

0 Pure 5% T 10% T 15% T 20% T

Wt %age reinforcement

Figure 5.3: Comparison of Impact Strength with %age variation of mixture Al O & SiC 2 3

Figure 5.1- 5.3 shows that with the increase in SiC & Al O constituent Impact strength is 2 3

increases w.r.t base metal. This is due to proper dispersion of SiC & Al O into the matrix or 2 3

strong interfacial bonding in between the Al alloy LM6 and SiC& Alumina inter faces.

40

5.2 HARDNESS TEST

A Rockwell hardness tester machine used for the hardness measurement. The sur face being

tested gener ally requires a metallographic finish and it was done with the help of 100, 220,

400, 600 and 1000 gr it size emery paper. Load used on Rockwell’s hardness tester was 200

grams at dwell time 20 seconds for each sample. The result of Rockwell’s hardness test for

simple alloy without r einforcement (Sample No.1) and the wt.% variation of different

reinforcements such as SiC/ Al O and Al alloy LM6 (Sample No. 2-13) are shown in Table 2 3

number 5.2.

Table 5.2: Results of hardness Test

Sample No Sample Name Hardness Mean Hardness

Rockwell Hardness LM 6 + Trial 1 Trial 2 Trial 3 Trial 4

1 Pure 53.7 52.7 54.5 51.9 53.2 2 2.5 % SiC 56.7 59.5 56.1 60.1 58.1 3 5 % SiC 50 48 53 51 51.0 4 7.5 % SiC 86.3 89.3 85.8 89.8 87.8 5 10 % SiC 91.2 90.7 91.7 91.3 91.2 6 2.5 % Al O 76.5 74.3 75.2 75.6 75.4

2 3 7 5 % Al O 85.2 83.2 86.6 86.6 85.4

2 3 8 7.5 % Al O 89.9 89.4 91.6 87.6 89.6

2 3 9 10 % Al O 91.6 98.8 92.5 101.3 95.8

2 3 10 2.5 + 2.5 % T 69.8 69.8 71.5 67.1 69.2 11 5 + 5 % T 85.9 85.6 85.4 85.8 85.6 12 7.5 + 7.5 % T 107.2 106.1 109.4 110.5 108.2 13 10 + 10 % T 119.0 122.0 118.0 121.0 120.0

100 90 80 70 60 50 40 30 20 10



Figure 5.4: Comparison the hardness with wt. % variation of SiC

41

120

100

80

60

40

20

0 Pure 2.5 % Al2O3 5 % Al2O3 7.5 % Al2O3 10 % Al2O3


Figure 5.5: Comparison the Hardness with wt. % variation of Al O 2 3

140

120

100

80

60

40

20

0 Pure 5 % T 10 % T 15 % T 20 % T


Figure 5.6: Comparison the Hardness with wt. % variation of combined Al O & SiC 2 3

In Figure number 5.4,5.5,5.6 results predict that unifor m increase in hardness is also seen.

This is due to increase in resistance to deformation by adding SiC and Alumina as

reinforcment in LM6 alloy.

5.3 TENSILE STRENGTH TEST

Tensile tests were used to assess the mechanical behavior of the composites and matrix alloy.

The composite and matrix alloy rods were machined to tensile specimens with a diameter of

6mm and gauge length of 30 mm. Ultimate tensile strength (UTS), often shortened to tensile

strength (TS) or ultimate strength, is the maximum stress that a material can withstand while

42

being stretched or pulled before necking, which is when the specimen's cross- section starts to

significantly contract.

Figure 5.7: Tensile Strength Specimens of different composition

Table 5.3: Tensile Strength Results

Alloy (LM6) Yield UTS Elongation (%)

Strength N/mm 2

N/mm 2

Pure 65 180 9

2.5% SiC 78 220 7.5

5% SiC 85 245 5.5

7.5% SiC 112 250 3.2

10% SiC 150 310 2.1

2.5 % Al O 75 190 8.1 2 3

5 % Al O 88 201 6.5 2 3

7.5 % Al O 105 250 3.9 2 3

10 % Al O 140 290 2.8 2 3

2. 5% SiC + 2.5 %Al O 100 240 6.8 2 3

5% SiC + 5 %Al O 170 270 4.5 2 3

7. 5% SiC + 7.5 %Al O 190 320 3.1 2 3

10 % SiC + 10 %Al O 220 370 1.4 2 3

5.3.1 Stress vs. Strain Curves

During tensile testing of a material sample, the stress–strain curve is a gr aphical

representation of the relationship between stress, der ived from measuring the load applied on

the sample, and strain, der ived from measuring the deformation of the sample, i.e. elongation,

compression, or distortion. The slope of stress-strain curve at any point is called the tangent

modulus; the slope of the elastic (linear) portion of the cur ve is a property used to

43

characterize materials and is known as the Young's modulus. The area under the elastic

portion of the curve is known as the modulus of resilience.

I. Stress vs. Strain Curves for Pure LM 6 Alloys

200

150

100

50

0 0 0.02 0.04 0.06 0.08 0.1

Strain

Figure 5.8: Stress vs. Strain Curves for LM 6 Alloys

II. Stress vs. Strain Curves for LM 6 Alloys with 2.5% SiC

250

200

150

100

50

0 0 0.02 0.04 0.06 0.08

Strain

Figure 5.9: Stress vs. Strain Curves for LM 6 Alloys with 2.5 % SiC

. III Stress vs. Strain Curves for LM 6 Alloys with 5% SiC

300 250 200 150 100

50 0

0 0.01 0.02 0.03 0.04 0.05 0.06

Strain

Figure 5.10: Stress vs. Strain Curves for LM 6 Alloys with 5 % SiC

44

. IV Stress vs. Strain Curves for LM 6 Alloys with 7.5% SiC

300

250

200

150

100

50

0 0 0.005 0.01 0.015 0.02 0.025 0.03 0.035

Strain

Figure 5.11: Stress vs. Strain Curves for LM 6 Alloys with 7.5 % SiC

V. Stress vs. Strain Curves for LM 6 Alloys with 10% SiC

250 200 150 100

50 0

0 0.02 0.04 0.06 0.08 0.1

Strain

Figure 5.12 : Stress vs. Strain Curves for LM 6 Alloys with 10% SiC

VI. Stress vs. Strain Curves for LM 6 Alloy with 2.5% Al O 2 3

250

200

150

100

50

0 0 0.02 0.04 0.06 0.08 0.1

Strain

Figure 5.13: Stress vs. Strain Curves for LM 6 Alloy with 2.5% Al O 2

45

VII. Stress vs. Strain Curves for LM 6 Alloy with 5% Al O 2 3

250 200 150 100

50 0

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Strain

Figure 5.14: Stress vs. Strain Curves for LM 6 Alloy with 5% Al O 2 3

VIII. Stress vs. Strain Curves for LM 6 Alloy with 7.5% Al O 2 3

300 250 200 150 100

50 0

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035

Strain

Figure 5.15 : Stress vs. Strain Curves for LM 6 Alloy with 7.5% Al O 2 3

IX. Stress vs. Strain Curves for LM 6 Alloy with 10% Al O 2 3

350 300 250 200 150 100

50 0

0 0.5 1 1.5 2 2.5

Strain

Figure 5.16: Stress vs. Strain Curves for LM 6 Alloy with 10% Al O 2 3

46

X. Stress vs. Strain Curves for LM 6 Alloy with 5% T (SiC & Al O ) 2 3

300 250 200 150 100

50 0

0 1 2 3 4 5 6 7

Strain

Figure 5.17: Stress vs. Strain Curves for LM 6 Alloy with 5% T (Sic & Al O ) 2 3

XI. Stress vs. Strain Curves for LM 6 Alloy with 10% (SiC &Al O ) 2 3

300

200

100

0 0 0.01 0.02 0.03 0.04 0.05

Strain

Figure 5.18 : Stress vs. Strain Curves for LM 6 Alloy with 10% T (SiC & Al O ) 2 3

XII. Stress vs. Strain Curves for LM 6 Alloy with 15% T (SiC & Al O ) 2 3

400

300

200

100

0 0 0.5 1 1.5 2 2.5 3 3.5

Strain


47

XIII. Stress vs. Strain Curves for LM 6 Alloy with 20%T (SiC & Al O ) 2 3

400 350 300 250 200 150 100

50 0

0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016

Strain


It exhibits a very linear stress–str ain relationship up to a well defined yield point. The linear

portion of the cur ve is the elastic region and the slope is the modulus of elasticity or Young's

Modulus. As defor mation continues, the stress increases on account of strain hardening until

it reaches the ultimate strength. Until this point, the cross-sectional area decreases unifor mly

because of Poisson contractions. The actual rupture point is in the same vertical line as the

visual rupture point. The work hardening rate increases with increasing volume fraction of

reinforcement ( and decreasing matrix volume). The lower ductility can be attributed to the

earlier onset of void nucleation with increasing amount of reinforcement.

48

5.3.2 Yield Strength Comparison

160

140

120

100

80

60

40

20

0 Pure 2.5% SiC 5% SiC 7.5% SiC 10% SiC

Wt % age Reinforcement

Figure 5.21: Comparison the Yield Strength with wt. % variation of SiC

160

140

120

100

80

60

40

20



Figure 5.22: Comparison the Yield Strength with wt. % variation of Al O 2 3

49

250

200

150

100

50

0 Pure 5 % T 10 % T 15 % T 20 % T

Wt % age Reinforcement

Figure 5.23: Comparison the Yield Strength with wt. % variation of Al O & SiC 2 3

As shown in Figure number 5.21,5.22,5.23 results predict that as the reinforcement wt.%

Yield Strength is increases. This happens may be due to dispersion of SiC & Alumina which

create hinderance to dislocation motion. To move this defect (plastically deforming or

yielding the mater ial), a larger str ess must be applied. This may results increase in tensile

strength of reinforced LM6 alloy.

50

5.3.3 Ultimate Tensile Strength Result

350

300

250

200

150

100

50

0 Pure 2.5% SiC 5% SiC 7.5% SiC 10% SiC

Fig. 5.24: Comparison of the Ultimate Tensile Strength with wt. % variation of SiC

350

300

250

200

150

100

50


Fig. 5.25: Comparison of the Ultimate Tensile Strength with wt. % variation of Al O 2 3

51

400

350

300

250

200

150

100

50

0 Pure 5 % T 10 % T 15 % T 20 % T

Figure 5.26: Comparison of the Ultimate Tensile Strength with wt. % variation of SiC & Al O mixture 2 3

As shown in Chart (Figure number 5.24,5.25,5.26) results predict that as the reinfor cement

wt.% UTS is also increases. This happens may be due to dispersion of SiC & Alumina which

create hinderance to dislocation motion. This may results increase in tensile strength of

reinforced LM6 alloy.

5.3.4 Length Elongation Comparison

10

8

6

4

2



Figure 5.27: Comparison the Elongation with wt. % variation of SiC

52

10 9 8 7 6 5 4 3 2 1 0

Pure 2.5 % Al2O3 5 % Al2O3 7.5 % Al2O3 10 % Al2O3


Figure 5.28: Comparison the Elongation with wt. % variation of Al O 2 3

10 9 8 7 6 5 4 3 2 1 0

Pure 5 % T 10 % T 15 % T 20 % T


Figure 5.29: Comparison the Elongation with wt. % variation of Mixture of SiC & Al O 2 3

As shown in Figure Number 5.27-5.29 results predict that as the wt. of SiC & Al O increases 2 3

elongation is decreases. This is due to decrease in ductility because of increase in tensile

strength as shown above.

53

5.4 RESULTS OF SEM

I. 2.5 % Alumina is mixed with LM6 Alloy

100 X 500 X 1000 X

Figure 5.30 : Microscopic View of 2.5 % SiC Reinforced in LM6 100 X, 500 X, 1000 X

II. 7.5 % SiC is Mixed with Alloy LM 6

100X 500 X 1000 X

Figure 5.31: Microscopic View of 7.5 % SiC Reinforced in LM6 100 X, 500 X, 1000X

III. 10 % Al O is mixed with Alloy LM 6 2 3

100 X 500 X 1000 X

Figure 5.32: Microscopic View of 10 % Alumina Reinforced 100 X, 500 X, 1000 X

IV. 7.5 % Al O and SiC with LM 6 2 3

100 X 500 X 1000 X

Figure 5.33: Microscopic View of 15 % SiC & Al O Reinforced in 100 X, 500 X, 1000 X 2 3

54

Figures 5.30, 5.31, 5.32, 5.33 are presented with the microphotographs of Cast LM 6-SiC and

Alumina composites respectively. From figures it can be observed that, the distributions of

reinforcements in the respective matrix are fairly uniform. Further these figures reveal the

homogeneity of the cast composites. The microphotograph also clear ly revels the increased

filler contents in the composites. Cracks are also seen in the microstructure.

5.5 XRD ANALYSIS RESULT

An X-ray diffraction (XRD) pattern of aluminium alloy matr ix composites and aluminium

alloy wer e shown in given f igure numbers 5.43- 5.51. X-ray diffraction of differ ent samples

was carried out by X’PERT PRO of PAN ANALYTI CAL using CuK a radiation. In XRD,

the physical content of the constituents pr esent in the samples are indicated in the for m of a

graphs and tables shows the name and percentage of element/ compound present in respective

Samples.

Figure 5.34: X-ray diffraction pattern of the alloy with 2.5% wt. SiC

55

Table 5.4: X-ray diffraction of the alloy with 2.5 % wt. SiC Ref.Code Score Compound Name Scale Factor Weight fraction (%)

01-089-2837 47 Aluminium 0.507 82.9

01-074-6395 47 Silicon 0.036 5.1

03-065-3163 12 Silicon Carbide 0.007 5.1

Figure 5.35: X-ray diffraction pattern of the alloy with 5% wt. SiC

Table 5.5: X-ray diffraction of the alloy with 5% wt. SiC Ref.Code Score Compound Name Scale Weight fraction (%)

Factor

01-075-0921 47 Aluminium 0.507 26

01-071-3901 47 Silicon 0.036 5.1

03-075-4411 12 Silicon Oxide 0.007 15

01-071-4624 20 Silicon .105 25

01-080-0369 21 Aluminium Oxide .075 19

01-067-0256 4 Silicon Oxide .123 13

56

Figure 5.36: X-ray diffraction pattern of the alloy with 7.5 % wt. SiC

Table 5.6: X-ray diffraction of the alloy with 7.5% wt. SiC

Ref.Code Score Compound Name Scale Weight fraction (%) Factor

01-074-6550 52 Silicon Oxide 0.606 32.5

01-089-3072 39 Aluminum Oxide 0.171 19.0

03-065-8554 11 Silicon Aluminum 0.013 30

01-073-1663 10 Silicon Carbide 0.031 4.5

01-077-1084 12 Silicon Carbide 0.008 4

57

Figure 5.37: X-ray diffraction pattern of the alloy with 10% wt. SiC

Table 5.7: X-ray diffraction of the alloy with 10% wt. SiC

Ref.Code Score Compound Scale Chemical Weight Fraction (%) Name Factor Formula

03-065-2869 48 Aluminium 0.606 Al 70.0

01-075-3170 39 Silicon Oxide 0.171 SiO 15.0 2

01-073-6302 16 Silicon Carbide 0.013 SiC 9.O

01-045-1363 8 Silicon 0.031 Si 1.0

58

Figure 5.38: X-ray diffraction pattern of the alloy with 2.5% wt. Al O

2 3

Table 5.8: X -ray diffraction pattern of the alloy with 2.5% wt. Al O 2 3

Ref.Code Score Compound Scale Weight fraction (%) Name Factor

01-071-4624 35 Aluminium 0.782 54.5

01-074-6395 12 Silicon 0.171 6

03-065-3163 3 Silicon Oxide 0.015 30

01-073-0368 5 Alumina Oxide 0.125 8

59

Figure 5.39: X-ray diffraction pattern of the alloy with 5% wt. Al O

2 3

Table 5.9: X-ray diffraction of the alloy with 5 % wt. Al O 2 3

Ref.Code Score Compound Name Scale Factor Weight fraction (%)

01-071-4624 19 Aluminium 0.868 54.5

01-074-6395 7 Silicon 0.171 6

03-065-3163 3 Silicon Oxide 0.013 30

01-073-0368 4 Alumina Oxide 0.031 5.1

60

Figure 5.40: X-ray diffraction pattern of the alloy with 7.5 % wt. Al O

2 3

Table 5.10- X-ray diffraction of the alloy with 7.5 % wt. Al O 2 3

Ref.Code Score Compound Name Scale Factor Chemical Formula Weight fraction (%)

01-089-2837 53 Aluminium 0.606 Al 5

01-089-2955 24 Silicon 0.171 SiO 81.2 2

01-075-1541 13 Alumina Oxide 0.013 SiC 12

01-079-1913 2 Silicon Oxide 0.031 Si 1.0

61

Figure 5.41: X-ray diffraction pattern of the alloy with 10 % wt. Al O

2 3

Table 5.11: X-ray diffraction pattern of the alloy with 10 % wt. Al O 2 3


01-089-2837 33 Aluminium 0.606 Al 4

01-089-2955 44 Silicon 0.171 SiO 81.2 2


01-079-1913 3 Silicon Oxide 0.031 Si 2.0

62

Figure 5.42: X-ray diffraction pattern of the alloy with 5% wt. SiC & Al O

2 3

Table 5.12: X-ray diffraction of the alloy with 5% wt. SiC & Al O 2 3

Ref.Code Score Compound Name Scale Chemical Formula Weight fraction (%) Factor

01-089-2837 33 Alumina Oxide 0.678 AlO 81.2 2

01-089-2955 44 Aluminium 0.052 Al 6

01-075-1541 4 Silicon Oxide 0.034 SiO 11 2

01-079-1913 3 Silicon 0.035 Si 4

63

Figure 5.43: X-ray diffraction pattern of the alloys with 10% wt. Al O & SiC

2 3 \

Table 5.13: X-ray diffraction pattern of the alloys with 10 % wt. Al O SiC 2 3 & \


01-076-2837 33 Alumina Oxide 0.678 AlO 75 2

01-065-2955 44 Aluminium 0.052 Al 18

01-085-1541 4 Silicon Oxide 0.034 SiC 2

01-099-1913 3 Silicon 0.035 Si 1

64

Figure 5.44: X ray diffraction pattern of the alloy with 15 % wt. of SiC & Al O

2 3

Table 5.14: X-ray diffraction pattern of the alloy with 15 % wt. of SiC & Al O 2 3


01-056-8554 37 Silicon Aluminium 0.567 SiAl 45

01-067-2339 48 Silicon 0.271 SiO 12 2


01-089-1916 7 Silicon Oxide 0.031 Si 11


65

Figure 5.45: X-ray diffraction pattern of the alloy with 20% of SiC & Al O 2 3

Table 5.15: X-ray diffraction pattern of the alloy with 20 % wt. of SiC & Al O 2 3


01-086-8554 33 Silicon Aluminium 0.606 Al 69

01-086-2339 44 Silicon 0.171 SiO 12 2


01-079-1916 3 Silicon Oxide 0.031 Si 8.0

In X-ray diffraction (Figur e. 5.45), eleven peaks have been obtained in the 2 span ranging

from 10 to 90. Applying extinction rules, these peaks and associated d-values have been

found to correspond to the aluminium matrix composite are given in Table 5.15. The peaks in

the pattern can be indexed to a mixture of dif ferent compounds such as Al, SiC and Al O . 2 3

Minor peaks attributed to impurity.

66

CHAPTER 6 CONCLUSIONS

6.1 CONCLUSIONS

The conclusions drawn from the present investigation are as follows:

1. The results confirmed that stir formed Al alloy LM 6 with SiC/Al O reinforced 2 3

composites is clearly superior to base Al alloy LM 6 in the comparison of tensile

strength, Impact strength as well as Hardness.

2. Dispersion of SiC/Al O particles in aluminium matr ix improves the hardness of the 2 3

matrix material.

3. It is found that elongation tends to decrease with increasing particles wt. percentage,

which confirms that silicon carbide and alumina addition increases brittleness.

4. Aluminium matrix composites have been successfully fabricated by stir casting

technique with fair ly uniform distribution of SiC & Al O particles. 2 3

5. It appears from this study that UTS and Yield strength trend starts increases with

incr ease in weight percentage of SiC and Al O in the matr ix. 2 3

6. The Hardness increases after addition of SiC, Al O particles in the matrix. 2 3

7. XRD results showed the presence SiC, Al O particles in alloy matrix. The oxide 2 3

phases like Al O and SiO etc. have dispersed uniformly throughout in the MMC thus 2 3

strengthening the resulting composite.

8. Impact strength is increase by adding SiC & Al O 2 3.

9. Stir casting process, stirrer design and position, stirring speed and time, particle-

preheating temperature, particle incorporation rate etc. are the important process

parameters.

6.2 SCOPE OF FUTURE WORK

1. This can further be extended by var ying geometr ical angle of Stirrer & by varying stirring

speed.

2. Heat treatment can be done to improve the properties.

3. Results can be var ied by var ying reinfor cement Grain Size.

67

REFERENCES

[1] Hashim J et al., “ Metal matrix composites: production by the stir casting method” ,

Journal of Materials Processing Technology 92-93 (1999) 1-7.

[2] http://en.wikipedia.org/wiki/Aluminium.htm on date 1/4/ 2011

[3] http://www.eaa.net/eaa/education/TALAT/index.htm on date 6/5/2011.

[4] Seymour G. Epstein, “ Aluminum and Its Alloys” , the Aluminum Association, Inc. 2001

[5] http://www.azom.com/article.aspx?ArticleID=310 on date 7/4/2011

[6] J. R. Davis, “ Aluminum and aluminum alloys”, ASM International, 1993

, “Effect of thermal ageing on Al-SiC Metal Matrix” [7] Sanjeev kumar , ME Thesis Thapar

University Patiala, 2010.

[8] Sudipt Kumar et al, “ production and characterisation of Aluminium-Fly Composites

using Stir Casting Method” , Department of Metallurgical & Materials Engineer ing National

Institute of Technology Rour kela, 2008.

[9]http://www.substech.com/dokuwiki/doku.php?id=liquid_state_fabrication_of_metal_matri

x_composites.htp on date 15/4/2011

[10] DIVECHA, A P et al, “ Silicon carbide reinforced aluminum - A formable composite”

Journal of Metals. Vol. 33, pp. 12-17. Sept. 1981

[11] C. M. Friend, “ The effect of matrix properties on reinforcement in short alumina fibre-

aluminium metal matrix composites” Journal of Mater ials Science ,Volume 22, Number 8,

3005-3010,Journal of Materials Science Volume 22, Number 8, 3005-3010, DOI:

10.1007/BF01086505

[12] N. Chawla et al, “ Tensile and fatigue fracture of Discontinuously Reinforced Aluminum ”

D, Advances in Fracture Research , (2001), pp. 1- 6.

[13] D Tabor, “The hardness of metals” Oxford University Press, 1951

[14] Toshir o Kobayashi,” Springer, 2004 - Technology & Engineering - 275 pages”

[15] http://www.mrl.ucsb.edu/mrl/centralfacilities/xray/xray-basics/index.htm, 11/5/2011.

[16] Joseph Goldstein, Scanning electron microscopy and x-ray microanalysis, Plenum

Publishers, 2001.

68

[17] Manoj Singla, “ Development of Aluminium Based Silicon Carbide Particulate Metal

Matrix Composite”, Journal of Minerals & Materials Characterization & Engineer ing, Vol. 8,

No.6, pp 455-467, 2009.

[18] I.A.Ibrahim et al, “ Particulate reinforced metal matrix composites - a review” , Jour nal

of mater ials science 26 (1991) 1137- 1156.

[19] D.J.Lloyd, “ Particle reinforced aluminium and magnesium matrix composites” ,

International Materials Reviews 1994 Vol. 39 No.1.

[20] L.Ceschini, “ Tensile and fatigue properties of the AA6061/20% volume Al O p and 2 3

AA7005/10% volume Al O p composites”, Composites Science and Technology 66 (2006) 2 3

333–342.

[21] S.V. Prasad, “ Aluminum metal–matrix composites for automotive applications:

tribological considerations”, Tribology Letters, Vol. 17, No. 3, October 2004.

[22] P.K. Rohatgi et al, “ Scatter and Statistical Analysis of Tensile Properties of Cast SiC

”, Materials Science and Engineering A, vol. 398, Issues 1- 2, Pages Reinforced A359 Alloys

1-14, April 2005.

[23] S. Balasivanandha Prabu, “ Influence of stirring speed and stirring time on distribution

of particles in cast metal matrix composite”, Journal of Materials Processing Technology

171 (2006) 268–273.

[24] M. Kok, “ Production and mechanical properties of Al O particle-reinforced 2024 2 3

aluminium alloy composites”, Journal of Materials Processing Technology 161 (2005) 381–

387.

[25] G.B.Veeresh Kumar, “ Studies on Al6061-SiC and Al7075-Al O Metal M atrix 2 3

Composites”, Jour nal of Minerals & Materials Characterization & Engineering, Vol. 9, No.1,

pp.43-55, 2010.

[26] Daniel.Miracle, “ Aeronautical Applications of Metal-Matrix Composites”, Air Force

Research Labor atory, Light Met. Age, Vol 57 (No. 1, 2) , 1999, p 117–121.

[27] A.Daouda, “ I nfluence of Al2O3 particulate on the ageing response of A356 Al-based

composites” , Journal of Materials Processing Technology 123 (2002) 313–318.

[28] W.Q. Song, P. Krauklis, A.P. Mouritz, S. Bandyopadhyay, “ The effect of thermal ageing

on the abrasive wear behaviour of age-hardening 2014 Al/SiC and 6061 Al/SiC composites” ,

Wear, Volume 185, Issues 1-2, June 1995.

69

[29] Z. M. El-Bradie, A. N. Abd El-Azim, “ Ageing behavior of aluminium alloy Glass

particulate composites” , Journal of Materials Processing Technology, Volume 66, Issues 1-

3, April 1997.

70

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